1. Field of the Invention
The present invention relates to a precision cutting apparatus for cutting workpieces such as semiconductor wafers or ferrite pieces, and more specifically a precision cutting apparatus using two blades for the purpose of improving the efficiency with which the cutting apparatus can cut workpieces.
2. Description of Related Art
Japanese Patent 3-11601(B) shows such a dual-blade type of precision cutting apparatus for use in dicing semiconductor wafers. It has two parallel-arranged spindle units rotatably supported in their spindle housing, each spindle unit having a cutting blade mounted to the tip end of the rotary axis. The direction in which these spindle units are arranged is referred to as "Y"-axial direction.
In making step cutting of a semiconductor wafer such a dicing apparatus can be advantageously used; one of the two cutting blades is a "V"-edged blade for cutting a "V"-shaped groove, and the other is a sharp-edged (or "I"-edged) blade for cutting the bottom of the "V"-shaped groove forming a Y-shape in cross-section, thus separating the semiconductor wafer into a plurality of chips, each having a top chamfered in all sides.
Such parallel-arrangement of two spindle units in the cutting direction or "X"-axial direction (and hence the two cutting blades arranged side by side in the "X"-axial direction) requires the spindle units to move excessively for the inter-blade center distance beyond the semiconductor wafer after crossing the full length of the workpiece because otherwise, the following blade cannot cut the workpiece to its extremity on either side of the workpiece. Apparently the overrunning on either side of the workpiece (or extra amount of cutting stroke) will lower the cutting efficiency accordingly.